As crude petroleum rises from the reservoir, it passes through narrow openings, accompanied by water, gases and naturally occurring surfactants. The mixture is agitated as it is pumped up through the production tubing. Such conditions are favorable to the formation of crude petroleum emulsions. Oftentimes, wellbore solids are carried up and flushed out with the crude mixture. The wellbore solids, together with the naturally-occurring surfactants tend to stabilize the emulsions.
These petroleum emulsions cannot be processed further without first removing the major part of the water. The dehydration of petroleum emulsions is generally accomplished by techniques including, but not limited to, settling, heat treatments, centrifuging, by the application of electrical fields or by the addition of demulsifiers. Petroleum emulsions are usually too stable to be broken by the mechanical processes mentioned above. The use of chemical demulsifiers has proven more effective in resolving crude petroleum emulsions. The chemical demulsifiers exert a direct influence on the interfaces of the crude petroleum emulsions and cause a breaking or separation of the petroleum emulsions at lower temperatures and with shorter treatment times than if the demulsifiers are not used.
A large number of patents describe the preparation of chemical demulsifiers. This is largely due to the fact that petroleum emulsions vary in their compositions and characteristics depending on geographical locations. A demulsifier which works well with petroleum emulsions for one location may be ineffective in other locations.
A number of representative background patents will be mentioned briefly. De Merig revealed the use of sulfonated mineral oils as demulsifiers in U.S. Pat. No. 2,209,445. Various types of modified alkyd resins were introduced as demulsifiers in U.S. Pat. No. 2,214,783. U.S. Pat. Nos. 2,260,798 and 2,301,609 mention the use of nitrosophenol and nitrosoaromatic carboxylic acids. Blair revealed the use of alkanolamine esters in U.S. Pat. No. 2,423,563.
U.S. Pat. No. 2,457,634 discloses the use of a soap formed by the reaction of a mineral acid with a complex amine, the latter being the reaction product of formaldehyde, phenol and a non-aromatic secondary amine. U.S. Pat. Nos. 2,499,370 and 2,557,081 described processes for resolving crude petroleum emulsions which employ certain oxyalkylated phenol-aldehyde resins. Alkylene oxide condensates of various sorts are the subjects of U.S. Pat. Nos. 2,973,340; 2,552,528 through 2,552,534; 2,792,352 through 2,792,357; 3,383,326; 3,511,882; 4,502,977; 4,511,239; and 4,626,379. Also of interest as background technology in the area of alkylene oxide condensates are European Application Nos. 0,267,517; 0,147,743; 0,141,585; 0,299,348; 0,277,060; 0,264,755; 0,246,582; 0,222,587 and 0,209,850.
As noted, many emulsion breakers are very specific to certain areas and particular crude oil compositions. Most commercial emulsion breakers are formulations or blends of several chemicals. As the production field ages or more wells are put into production, new chemical or new blends may have to be put into the system.
Fireflooding is one of the thermal recovery methods. Heat is introduced into an oil reservoir through the injection of air into the reservoir and burning some of the oil in situ. By controlling the air injection and the amount of oil burned, the heat generated is kept within desired limits. The hot combustion gases generate flow toward the production wells, pushing or carrying the oil to the production zone.
Many types of demulsifiers, such as alkylene oxide condensates of various kinds and sulfonated compounds, have been applied in the field to resolve crude petroleum emulsions obtained from fireflooding with various degrees of success. For example, commodity chemical dodecylbenzenesulfonic acid (DDBSA) and its metallic salts have been used as emulsion breakers in some leases where oil is recovered through firefloods. In one lease in Canada, DDBSA was used in the system for a period of time. With age and as more wells were brought online, the emulsion characteristics changed sufficiently as to render the DDBSA ineffective.